1. Field of the invention
The present invention relates to a method of and apparatus for manufacturing small-size gas-filled lamps, particularly small-size halogen-gas-filled lamps, for use in optical instruments, medical instruments, electronic devices and the like.
2. Description of the Prior Art
It has been customary practice to manufacture small-size gas-filled lamps by sealing a bead attached a filament into a bulb manually with a gas burner, connecting the assembly to a vacuum source to develop a vacuum in the bulb, introducing a gas such as argon, nitrogen, or krypton, for example, into the bulb, and finally burning off the tip through which the air was discharged and the gas was filled, using a gas burner. According to a present mechanized manufacuring process, the manual steps are replaced with mechanical operations which are effected individually at angularly spaced positions around an indexing table as the latter intermittently rotates for thereby assembling lamps one by one.
There has been proposed a method of simultaneously manufacturing a multiplicity of small-size gas-filled lamps. With this method, a heater is attached to an outer wall of a tunnel-shaped chamber in which a vacuum is developed or a gas is introduced, bulbs and beads with filaments attached are mounted on jigs in the chamber, and the jigs are pulled along by a wire while the bulbs and beads are assembled into lamps. This method is however limited to applications where a gas at atmospheric pressure or lower pressure is filled.
The manual or mechanized fabrication process is normally performed in atmosphere. If the gas pressure in the lamp bulb were higher than atmospheric pressure, then the gas would be blown out when the tip is burned off after the gas has been filled. Therefore, it is impossible to fill gas at higher pressure in the lamp. If the tunnel-shaped chamber with the heater attached to its outer wall were heated, it would be highly dangerous since the chamber itself would be heated, and the jigs and the entire chamber would have to be heated. The gas filled in the lamp bulbs would then become poor in purity due to an impure gas generated by the heated chamber and jigs.
In the manufacture of halogen lamps or the like, the active gas such as halogen gas produces compounds through reaction with a furnace and jigs which are heated to high sealing temperature, and no prescribed percentage of halogen gas cannot be filled in lamps. To avoid this difficulty, it is current practice to make halogen-gas-filled lamps by fabricating bulb and filament assemblies one by one at angularly spaced positions around an indexing table according to the known mechanized process. After a halogen gas has been filled, the lamp introduction tube is sealed for a length greater than the required sealed portion, and then the lamp portion of the bulb is cooled by liquid nitrogen to transfer the halogen gas from the gas introduction tube into the bulb at an enriched state under a pressure lower than atmospheric pressure. Thereafter, the prescribed sealed portion is burned off by a gas burner.
As described above, the presently available methods of manufacturing small-size gas-filled lamps suffer from various problems, and have complicated steps. The lamps manufactured by such methods are unstable in quality. The methods have therefore been unsatisfactory for mass-producing lamps of good quality.